Design and Development of Two-Dimensional Strained Layer Superlattice (SLS) Detector Arrays for IR Applications

The implementation of strained layer superlattices (SLS) for detection of infrared (IR) radiation has enabled compact, high performance IR detectors and two-dimensional focal plane arrays (FPAs). Since initially proposed three decades ago, SLS detectors exploiting type II band structures existing in the InAs/GaSb material system have become integral components in high resolution thermal detection and imaging systems. The extensive technological progress occurring in this area is attributed in part to the band structure flexibility offered by the nearly lattice-matched InAs/AlSb/Ga(In)Sb material system, enabling the operating IR wavelength range to be tailored through adjustment of the constituent strained layer compositions and/or thicknesses. This has led to the development of many advanced type II SLS device concepts and architectures for low-noise detectors and FPAs operating from the short-wavelength infrared (SWIR) to very long-wavelength infrared (VLWIR) bands. These include double heterostructures and unipolar-barrier structures such as graded-gap M-, W-, and N-structures, nBn, pMp, and pBn detectors, and complementary barrier infrared detector (CBIRD) and pBiBn designs. These diverse type II SLS detector architectures have provided researchers with expanded capabilities to optimize detector and FPA performance to further benefit a broad range of electro-optical/IR applications

Progress in resonator quantum well infrared photodetector (R-QWIP) focal plane arrays

In this work, the performance of a 640 X 512 long-wavelength resonant quantum well infrared photodetector (R-QWIP) focal plane array (FPA) was evaluated as a function of operating temperature, bias, and photon flux using an F/2.2 optic. From these FPA measurements an assessment of the dark current, noise, conversion efficiency and noise-equivalent temperature difference is provided herein. Histogram results are used to support a statistical interpretation of operability and non-uniformity across the R-QWIP FPA. In addition, single pixel devices fabricated from the same wafer lot enabled supplemental noise gain and spectral response measurements. The spectral response of this R-QWIP structure was confirmed to peak around 8.3 microns with a spectral bandwidth or approximately 1 micron (full-width half maximum) and the noise gain measurements were used to provide an estimation of the expected external quantum efficiency (conversion efficiency = quantum efficiency ⁄ gain)